When debugging, PyCharm opens duplicate windows when stepping into a new module Follow

I keep my window split horizontally.  The code I'm developing is in the upper frame, unit tests in the lower.

When stepping through a unit test into a module that currently resides in the upper frame, PyCharm will open a new copy of the module in the lower frame.  

This worked as expected in 3.3, and started failing in 3.4.